The present invention relates to an automated tiering control for a storage system and containing a plurality of levels.
Larger data volumes and diversified types of data as well as a wide variety of storage media within storage devices due to the spread of high-speed SSD (Solid State Drives) that are faster than HDD (hard disk drive) has made the placing of data into the appropriate storage media tier (or level) a difficult task. One technique for resolving this issue is an automated storage tiering function for storage devices to automatically store the data in the appropriate storage media according to the access frequency of occurrence of the data.
An automated tiering control function generally migrates the page to an upper tier (or level) (called promotion) when there is a large IO (input/output) frequency of occurrence on a page, and migrates the page to a lower tier (or level) (called demotion) when there is a small IO frequency of occurrence within a fixed cycle (load monitoring measurement period.) There is also a technology (e.g. US Patent Application Publication No. 2012/0246386A1) that samples two types of exponential moving averages (a value increasing-diminishing within a few cycles, and a value increasing-diminishing within many cycles) rewritten during the above cycle interval, and combines these two types of values, setting one index value or namely the IO frequency of occurrence (load index) in order to account for IO fluctuations within a short cycle.